The use of electric arc furnaces in metallurgy, both ferrous and non-ferrous, has been increasing at a substantial rate. In the electric arc furnace process, graphite electrodes are consumed. Electrode consumption rates vary greatly from electrode to electrode and can vary, for example, from 3 to 25 pounds per ton of metal (e.g., steel, iron, copper). Thus, the consumption of graphite electrodes has also been increasing at a substantial rate. The cost of the graphite electrode generally is from about 7 to 12 percent of the total raw material cost charged into the electric furnace and is thus a significant cost variable in this type of process.
One of the disadvantageous features of graphite electrodes for use in electric arc metallurgical furnaces is the inability to predict the consumption rate of a given electrode. That is, while a group of electrodes may be produced in the same manner and may visually be essentially identical, the consumption rate of one electrode may be twice that of another electrode within the same group.
It would be desirable to have a standard, minimum consumption rate (for example, a minimum consumption rate for a particular type and size of electrode). However, there is presently no method of determining how long an electrode will last in use other than the actual consumption rate itself. The need exists for a method of determining, before a particular electrode is used, the approximate consumption rate.
In recent years, attempts have been made to correlate various physical properties of the electrodes used in the electric arc metallurgical furnaces with consumption rate. The properties generally considered have included density, mechanical strength, modulus of elasticity, thermal conductivity, electrical resistivity, oxidation rate and apparent porosity. In these investigations, samples are generally taken from the socket end of the electrode and the various properties measured. However, the results obtained have not satisfactorily equated any or all of these properties with the consumption rate. In addition, the proposed method is destructive of the electrode itself (or at least a part of the electrode) and requires a relatively skilled technician and/or extensive laboratory equipment.